This invention relates to a fuel injection control system for an internal combustion engine and more particularly to an improved control system and routine for controlling fuel injection.
A wide variety of types of controls for fuel injection for internal combustion engines have been proposed. These controls generally sense one or more engine parameters and then set the amount of fuel injected in response to the sensed parameters. This setting is normally done by the measuring of the running conditions and then the selection of the fuel injection amount from a map generated from actual running conditions and the fuel required for each running condition. Although these systems are generally quite accurate, they do have some disadvantages.
For example, one parameter that is frequently measured is air flow to the engine. There are various types of air flow sensors which have been employed. For example, one type of air flow sensor is the so-called hot wire type that has a wire positioned across the intake opening of the engine and which is electrically heated. The temperature of the wire is indicative of air flow. In addition, various flap type valve devices have also been proposed for measuring air flow. These devices have the disadvantage of necessitating placement in the induction passage and thus reducing air flow. In addition, the characteristics of the air flow meter may change from time to time.
Another way of measuring air flow in two cycle engines consists of measuring the pressure in the crankcase chamber at different times and deriving the air flow from the pressure differences. This system can be quite accurate under many running conditions. Various other devices have been provided for measuring the air flow to an engine.
The problem with most air flow measuring systems is that they may be very accurate at a certain range of operation, however, their accuracy can be not as good as other types of devices under other running conditions. As a result, the amount of fuel supplied under the conditions when the measuring device is not as accurate will also be inaccurate.
It is, therefore, a principal object of this invention to provide an improved fuel injection control system that is capable of measuring the same condition by different methods in order to provide better accuracy throughout the entire engine running conditions.
It is a further object of this invention to provide a fuel injection control system for an engine wherein a given running parameter is sensed in two different manners and the most accurate manner is chosen to control the amount of fuel injected under the particular running condition.
It is a further object of this invention to provide an improved fuel injection control for an internal combustion engine that measures air flow to the engine in two different manners, one of which has more accuracy under certain running conditions than the other and selecting the most accurate measurement to control the fuel for a given running condition.
As has been noted, various devices have been proposed for measuring engine conditions to control the amount of fuel injected to an engine. Frequently systems incorporate malfunction sensors which determine when a sensor is giving a false signal and the system then goes to a failure mode. Generally these failure modes provide a fixed amount of fuel regardless of the actual running condition when the sensor fails. Obviously this type of system has a number of disadvantages.
It is, therefore, a still further object of this invention to provide an improved fuel injection system that has two sensors for sensing a given running condition and wherein the control is shifted from one sensor to the other in the event the one sensor is determined to have failed.
As previously noted, it is desirable to include some form of system for determining a failure of a sensor in a fuel injection control so as to provide compensation in the event of sensor failure. One way that sensor failures are determined is if the sensor outputs a signal that is clearly indicative of an abnormal condition. It is, obviously, desirable to ensure against inadvertent shifting into the failure mode in the event the sensor has not actually failed. As a result, the abnormal condition which indicates a failure is normally chosen as one which is far outside of the range of normal conditions. This will insure against false failure signals. However, it will also provide a situation wherein the sensor has failed but not so severely as to indicate a failure mode and inadequate fuel control will result.
If the tolerance of acceptable values from the sensor is set too low, however, then a failure mode may be indicated when failure has not actually occurred. That is, even an engine running under normal conditions can produce some variations in running condition signals without there necessarily being a failure in the sensor.
It is, therefore, a still further object of this invention to provide an improved method for detecting a sensor failure in a fuel injection system.
It is a further object of this invention to provide a method of sensing failure of a sensor in a fuel injection system that indicates a failure mode when the sensor deviates from a normal output for a certain percentage of its output signals.
As just discussed, the engine conditions can vary significantly from one cycle to the next even though the basic running condition of the engine is unchanged. That is, even during normal running of the engine there will be some variations from cycle to cycle. Hence, if the sensor senses the operation or condition at only a single cycle and this determines the amount of fuel supplied, there can be errors in the amount of fuel supplied to the engine.
It is, therefore, a still further object of this invention to provide an improved condition sensing arrangement for a fuel injection control.
It is a further object of this invention to provide an engine sensing condition for a fuel injection control wherein the sensed conditions are measured over a number of cycles and the control is based upon the average of the sensed conditions. This information is then updated on each cycle.